1. Field of the Invention
The present invention relates to an image-capturing technology, and more particularly to an apparatus and method of capturing images having an optimized quality under night scene conditions.
2. Description of the Prior Art
With the increasing use of diverse image devices such as a digital still cameras, phone cameras, digital single-lens reflex (DSLR) cameras, and so forth, ordinary users are increasingly demanding high quality images like those used by professionals.
In the case of capturing an image of an object using such an imaging device, however, image regions, which cannot be covered through automatic exposure control (AE), may be produced in special environments such as environments having back-lighting, low illumination, high contrast, and so forth.
In order to solve this problem, a method using an HDR (High Dynamic Range) sensor, and a method of capturing and synthesizing a plurality of images have been proposed. However, these methods have other problems such as design difficulty, increased manufacturing costs, and others.
Particularly, although there is a high demand for capturing high-quality images in low-illumination environments such as night scenes, most camera users have difficulty capturing high-quality images. In low-illumination environments, professional photographers use a method of securing a sufficient quantity of light by fixing a camera using a tripod and using a long exposure.
However, since general camera users usually do not use tripods, the long exposure for securing the quantity of light heightens the blur level of the image, which decreases the quality of the image. By contrast, the professional photographers learn by experience the exposure time suitable for inferior environments by properly considering the environment surrounding the object and the amount of camera shake that occurs without a tripod.
Generally, according to custom of camera manufacturers, the shutter speed is set to about ⅛ second in the case where shake compensation is performed using an optical image stabilizer (OIS), while in the case where no OIS is provided, the shutter speed is set to about 1/30 second.
However, such a uniform setting of the exposure time may make it impossible to generate a high-quality image of a specialist level that is suitable to diverse environments. Although the problems that an autofocus camera has in capturing the night scenes have been continuously raised, no solution has been proposed.
Accordingly, in addition to the existing method of compensating for the image blur by moving an optical system or an image sensor using sensor information such as optical image stabilization (OIS), there is a need for a method and apparatus for an adaptive exposure adjustment by sensing whether the present environment is a night scene.